We have, in previous studies, made the discovery that generalized transducing Salmonella phage can recombine with various unrelated bacteriophages to evolve into new hybrid phage species. Recently, we isolated an unusual Salmonella typhimurium-E. coli hybrid with sensitivity to coliphage gamma and Salmonella phage P22. This bacterial strain and its derivatives have facilitated construction of new hybrid phage species between the evolutionary diverse phage gamma, which has a unique genome, and phage P22 which has a circularly permuted genome. Similarly hybrids between coli phage phi 80 and P22 phage and hybrids between coli mutator phage Mu-1 and P22 were isolated. These hybrid phages provide an excellent model for studying a mechanism of genetic evolution, control of gene expression within gene clusters derived from diverse phages, phage morphogenesis, phage chromosome structure, antigen conversion and nature of transduction. To study the above mechanisms, we propose the following: (1) Isolation of repressor molecules of P22 and gamma, their in vitro binding to P22-gamma and gamma-P22 DNAs, and their effects on in vitro transcription; (2) Isolation and characterization of gamma rep gene product; (3) Restriction endonuclease analysis of DNA from gamma-P22, P22-gamma and phi 80-P22 hybrid phages to determine the origin of DNA segments; (4) Creation of morphological chimera via mutation of gamma-P22dis; (5) Attempts to isolate a Salmonella mutator phage, P22-Mu, a hybrid between Salmonella phage P22 and E. coli mutator phage Mu-1.